1. Field of the Invention
The present invention relates to an optical pickup apparatus configured to perform an operation of reading a signal recorded in an optical disc and an operation of recording a signal in an optical disc by a laser beam.
2. Description of the Related Art
Optical disc devices have been widespread each of which is configured to irradiate a signal recording layer of an optical disc with a laser beam emitted from an optical pickup apparatus, to perform a signal reproduction operation and a signal recording operation.
The optical disc devices, which employ optical discs called CD or DVD, are generally spread, but those employing optical discs with improved recording density, that is, optical discs of the Blu-ray standard, have been developed. As the laser beam with which a reading operation of a signal recorded in an optical disc of the Blu-ray standard is performed, a laser beam having a short wavelength, e.g., a blue-violet light having a wavelength of 405 nm, is used.
An optical pickup apparatus is configured to collect a laser beam emitted from a laser diode onto a signal recording layer provided in an optical disc by a light collecting operation of an objective lens, as well as to irradiate a photodetector with return light, which is a laser reflected from the signal recording layer. That is, a focus error signal or a tracking error signal is generated from a signal obtained with a change in light amount or a change in position of the laser beam applied to a quadrant sensor or the like included in the photodetector, and a displacement position of the objective lens is controlled using these signals, so that the operation of reading a signal recorded in the optical disc and the like is performed.
In the optical pickup apparatus configured to perform such operations, not only the photodetector but also a light-emitting surface of the laser diode is irradiated with the return light reflected from the signal recording layer. If the light-emitting surface of the laser diode is irradiated with the return light, the laser beam is modulated, which causes a problem of a phenomenon called laser beam noise.
As a method of solving such a problem caused by the return light, a method of superimposing a high-frequency signal on a driving signal of the laser diode is commonly adopted. Such a method is called a high-frequency superimposing method, and since a spectrum of a laser beam emitted from a laser diode can be made into a multimode by superimposition of a high frequency current, coherence of the laser beam can be reduced, and as a result, laser beam noise caused by reflected light from an optical disc can be reduced.
Japanese Patent Laid-Open Publication No. 2004-192705 as Patent Document describes such an art as to be configured so that a superimposition IC that generates a high-frequency signal is arranged on a flexible wiring board and a high-frequency signal is supplied to a laser diode that is fixed to the flexible board via a wiring pattern formed on the flexible board.
In such a configuration, since the length of a wiring pattern WR, through which the high-frequency signal flows, is long, thereby causing a problem that so-called unnecessary radiation occurs, that is, an unnecessary signal that adversely affects other circuits is emitted from the wiring pattern.
FIG. 9 illustrates an outline of the above-described configuration in which a laser diode 100 is fixed to a flexible wiring board FS1. A lead terminal L extending from this laser diode 100 is soldered to the wiring board FS1, and a flexible sheet FS2 is prepared, which is integral with or separate from the wiring board FS1. The whole of the flexible sheet FS2 is formed in an elongated shape, a wide width portion W is formed in the middle, and a high-frequency superimposition integrated circuit (hereinafter referred to as a superimposition IC) (P1) is mounted to the wide width portion W.
The laser diode 100 is bonded and fixed to a plastic housing, and the other end of this flexible sheet FS2 is folded and soldered to a printed board provided on the back side of the housing.
As described above, since the flexible sheet FS2 is provided in an elongated state and a high-frequency signal flows through the wiring, unnecessary radiation is emitted. Further, a loop circuit or the like is configured, thereby causing a problem that electromagnetic noise is received therein or emitted therefrom.